The specter of a blood pressure J curve arose again last week at the ACC meeting in an analysis of 5,000 patients with diabetes and coronary artery disease in the INVEST trial, who showed a clear, increased rate of death when their antihypertensive treatment dropped their systolic blood pressure below 115 mm Hg (see photo)

One of the best recent analyses to show evidence for the J curve was a 2006 report that used data collected in that same 22,000-patient INVEST study, although the older analysis used data from all patients, not just the ones with diabetes, and focused on the link between low diastolic pressure and both death and myocardial infarction. The 2006 report said that patients faced risk when their diastolic pressure fell below 70 mm Hg.

The reason why excessively low pressure can be deadly isn’t clear, but possible explanations include low blood flow to critical organs such as the kidney and brain, or that low pressures are markers for patients with severe underlying illness or advanced vascular disease. These mechanisms probably depend more on low diastolic pressure, but, of course, when systolic pressure is low diastolic usually is too.

Whatever the reason, the finding is a reminder that it’s important for physicians to focus not on simply getting a patient’s blood pressure low, but on getting it within a target range. As one INVEST collaborator told me, “My guess is that on follow-up patients were lower, but their physicians made no adjustment [in their antihypertensive dosages] unless the patients complained of symptoms.”

It’s tempting to speculate that results of the ACCORD blood pressure trial, also reported at the ACC meeting–which showed that getting patients with diabetes to an average systolic pressure of 119 mm Hg led to no better outcome than in patients kept at an average of 133 mm Hg–occurred not because a systolic pressure of 133 mm Hg is ideal but because too many patients in the tight-control group had systolic and diastolic pressures that ran below 115/70 mm Hg. It’s quite possible that the detrimental effects of excessively low pressures masked the benefit from systolic pressures in the 120-130 mm Hg range.

My full report on the ACCORD blood pressure and INVEST studies at the ACC meeting is here.